Method for manufacturing nonaqueous secondary battery

Abstract

To provide a method for manufacturing a nonaqueous secondary battery, the method enabling suppression of deterioration in peeling strength of a negative electrode body.SOLUTION: A nonaqueous secondary battery has a positive electrode sheet, a negative electrode sheet 24, and a nonaqueous electrolyte. A method for manufacturing a nonaqueous secondary battery includes: a coating step to manufacture the negative electrode sheet 24 by coating a negative electrode composite layer 26 including a negative electrode active material 31 and lithium salt 32 to the a negative electrode current collector 25; and a liquid injection step to inject a nonaqueous electrolyte containing no film forming material containing the lithium salt into a battery case housing the positive electrode sheet and the negative electrode sheet 24. In the coating step, coating is performed in such a manner that the amount of the lithium salt 32 included in the negative electrode composite layer 26 becomes smaller on a surface side of the negative electrode composite layer 26 than on the current collector side close to the negative electrode current collector 25.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a method for producing a non-aqueous secondary battery. [Background technology]

[0002] In the method for producing a non-aqueous secondary battery described in Patent Document 1, a composition containing a negative electrode active material and lithium bis(oxalato)borate (LiBOB), which is an example of a lithium salt, is applied onto a negative electrode current collector to produce a negative electrode body, and the negative electrode body and a non-aqueous electrolyte are housed in a battery case. Note that the non-aqueous electrolyte does not contain a lithium salt. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-41567 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the method for producing a nonaqueous secondary battery described in Patent Document 1, when a nonaqueous electrolyte solution not including a film-forming material including a lithium salt is poured into a battery case containing a negative electrode body, the lithium salt present near the surface of the negative electrode body comes into contact with the nonaqueous electrolyte solution and dissolves. Then, the lithium salt moves to the center of the negative electrode body, so that the concentration of lithium salt at the end of the negative electrode body decreases, and the film derived from lithium salt at the end of the negative electrode body becomes thinner. It is required to suppress the decrease in the peel strength of the negative electrode body due to the decrease in uniformity of the film derived from lithium salt of the negative electrode body. [Means for solving the problem]

[0005] A method for producing a nonaqueous secondary battery that solves the above-mentioned problems is a method for producing a nonaqueous secondary battery having a positive electrode sheet, a negative electrode sheet, and a nonaqueous electrolyte, and includes a coating step of producing the negative electrode sheet by coating a negative electrode substrate with a negative electrode composite layer containing a negative electrode active material and a lithium salt, and a liquid injection step of injecting the nonaqueous electrolyte that does not contain a coating material containing the lithium salt into a battery case that contains the positive electrode sheet and the negative electrode sheet, wherein in the coating step, coating is performed such that the amount of lithium salt contained in the negative electrode composite layer is smaller on the surface side of the negative electrode composite layer than on the substrate side closer to the negative electrode substrate.

[0006] According to the above method, the amount of lithium salt contained in the negative electrode mixture layer is less on the surface side of the negative electrode mixture layer than on the substrate side closer to the negative electrode substrate. Therefore, when a non-aqueous electrolyte solution that does not contain a coating material containing lithium salt is poured into a battery case, the lithium salt on the surface side of the negative electrode mixture layer can be prevented from migrating from the end to the center of the negative electrode sheet by the non-aqueous electrolyte solution. The lithium salt moves from the negative electrode mixture layer on the substrate side closer to the negative electrode substrate to the surface side, improving the uniformity of the coating derived from the lithium salt of the negative electrode sheet. Therefore, the peel strength of the negative electrode mixture layer can be prevented from decreasing.

[0007] In the method for producing a nonaqueous secondary battery, it is preferable that the lithium salt is not contained on the surface side of the negative electrode mixture layer. According to the above method, the surface side of the negative electrode mixture layer does not contain lithium salt, and therefore unevenness in the coating film formed on the surface of the negative electrode mixture layer due to lithium salt can be suppressed.

[0008] In the above-described method for producing a nonaqueous secondary battery, the coating step preferably includes a first coating step of coating a first negative electrode composite layer containing the lithium salt onto the negative electrode base material, and a second coating step of coating a second negative electrode composite layer, the second negative electrode composite layer having a smaller amount of lithium salt than the first negative electrode composite layer, onto the first negative electrode composite layer.

[0009] The method includes a first coating step of coating a first negative electrode composite layer onto a negative electrode substrate, and a second coating step of coating a second negative electrode composite layer onto the first negative electrode composite layer, the second negative electrode composite layer having a smaller amount of lithium salt than the first negative electrode composite layer, so that the amount of lithium salt contained in the negative electrode composite layer can be easily changed for each coating step.

[0010] In the above method for producing a nonaqueous secondary battery, it is preferable that the second negative electrode mixture layer forms a surface of the negative electrode mixture layer and does not contain the lithium salt. According to the above method, the second negative electrode mixture layer that forms the surface of the negative electrode mixture layer does not contain lithium salt, which makes it possible to suppress unevenness in the coating that originates from lithium salt and is formed on the surface of the negative electrode mixture layer.

[0011] In the method for producing a nonaqueous secondary battery, the lithium salt preferably has a diameter that is 0.414 or less times the diameter of the negative electrode active material. According to the above method, the diameter of the lithium salt is 0.414 times or less the diameter of the negative electrode active material, which makes it possible to suppress a decrease in the peel strength of the coating resulting from the lithium salt. Effect of the Invention

[0012] According to the present invention, it is possible to suppress a decrease in the peel strength of the negative electrode mixture layer. [Brief description of the drawings]

[0013] [Figure 1] 1 is a perspective view showing a schematic configuration of a cell battery of an embodiment of a nonaqueous secondary battery. [Diagram 2] FIG. 4 is a view showing a part of the electrode body of the embodiment in an expanded form. [Diagram 3] 3A to 3C are diagrams illustrating a method for manufacturing the nonaqueous secondary battery according to the embodiment. [Figure 4] 3A to 3C are diagrams illustrating a method for manufacturing the nonaqueous secondary battery according to the embodiment. [Diagram 5] 3A to 3C are diagrams illustrating a method for manufacturing the nonaqueous secondary battery according to the embodiment. [Figure 6]3A to 3C are diagrams illustrating a method for manufacturing the nonaqueous secondary battery according to the embodiment. [Figure 7] 10A to 10C are diagrams illustrating a manufacturing method of a modified example of a nonaqueous secondary battery. [Figure 8] 1 is a table showing examples and comparative examples of nonaqueous secondary batteries. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] [Present embodiment] An embodiment of a method for producing a nonaqueous secondary battery will be described below with reference to Figures 1 to 6. As an example of the nonaqueous secondary battery, a lithium ion secondary battery will be described.

[0015] [Lithium-ion secondary battery 10] 1, a lithium-ion secondary battery 10 is a cell battery that is combined with a plurality of lithium-ion secondary batteries 10 and sealed in a resin or metal case to form a battery pack. The battery pack is used in hybrid vehicles and electric vehicles.

[0016] The lithium ion secondary battery 10 includes a battery case 11 and a lid 12. The battery case 11 has a rectangular parallelepiped shape with an opening on the upper side. The lid 12 seals the opening of the battery case 11. The battery case 11 and the lid 12 are made of a metal such as aluminum or an aluminum alloy. The lithium ion secondary battery 10 is configured as a sealed battery container by attaching the lid 12 to the battery case 11.

[0017] The lid 12 is provided with two positive external terminals 13A and a negative external terminal 13B. The positive external terminal 13A and the negative external terminal 13B are used for charging and discharging power. The electrode body 20 is accommodated inside the battery case 11. The positive electrode side current collector 20A, which is the end of the electrode body 20 on the positive electrode side, is electrically connected to the positive external terminal 13A via the positive electrode side current collector 14A. The negative electrode side current collector 20B, which is the end of the electrode body 20 on the negative electrode side, is electrically connected to the negative external terminal 13B via the negative electrode side current collector 14B. In addition, a nonaqueous electrolyte is injected into the battery case 11 through a liquid injection hole (not shown). The shapes of the positive electrode external terminal 13A and the negative electrode external terminal 13B are not limited to those shown in FIG. 1 and may be any shape.

[0018] [Electrode body 20] As shown in Fig. 2, the electrode body 20 is a flat wound body obtained by winding a laminate in which a long positive electrode sheet 21 and a negative electrode sheet 24 are stacked with a separator 27 interposed therebetween. The positive electrode sheet 21, the negative electrode sheet 24, and the separator 27 are stacked such that their respective longitudinal directions coincide with the longitudinal direction D1. In the laminate before winding, the positive electrode sheet 21, the separator 27, the negative electrode sheet 24, and the separator 27 are stacked in this order. The positive electrode sheet 21 is a positive electrode body, and the negative electrode sheet 24 is a negative electrode body.

[0019] [Positive electrode sheet 21] The positive electrode sheet 21 includes a positive electrode current collector 22 and a positive electrode composite layer 23. The positive electrode current collector 22 is a foil-like positive electrode base material formed in an elongated shape. The positive electrode composite layer 23 is provided on each of two opposing surfaces of the positive electrode current collector 22. The positive electrode current collector 22 includes a positive electrode-side uncoated portion 22A at one end in the width direction D2 where the positive electrode composite layer 23 is not formed and the positive electrode current collector 22 is exposed.

[0020] A metal foil made of aluminum or an alloy mainly composed of aluminum is used for the positive electrode current collector 22. The positive electrode current collector 22 functions as a current collector for the positive electrode. In the wound state, the positive electrode side uncoated portion 22A of the positive electrode current collector 22 is pressed against each other at opposing surfaces to form the positive electrode side current collector 20A.

[0021] The positive electrode mixture layer 23 is a hardened body of a liquid positive electrode mixture paste. The positive electrode mixture paste includes a positive electrode active material, a positive electrode solvent, a positive electrode conductive material, and a positive electrode binder. The positive electrode mixture layer 23 is formed by drying the positive electrode mixture paste and evaporating the positive electrode solvent. Therefore, the positive electrode mixture layer 23 includes a positive electrode active material, a positive electrode conductive material, and a positive electrode binder.

[0022] The positive electrode active material is a lithium-containing composite oxide capable of absorbing and releasing lithium ions, which are charge carriers in the lithium-ion secondary battery 10. The lithium-containing composite oxide is an oxide containing lithium and a metal element other than lithium. The metal element other than lithium is at least one selected from the group consisting of nickel, cobalt, manganese, vanadium, magnesium, molybdenum, niobium, titanium, tungsten, aluminum, and iron contained in the lithium-containing composite oxide as iron phosphate.

[0023] For example, lithium-containing composite oxides include lithium cobalt oxide (LiCoO 2 ), lithium nickel oxide (LiNiO 2 ), lithium manganate (LiMn 2 O 4 For example, the lithium-containing composite oxide is a ternary lithium-containing composite oxide containing nickel, cobalt, and manganese, and is lithium nickel cobalt manganese oxide (LiNiCoMnO 2 For example, the lithium-containing composite oxide is lithium iron phosphate (LiFePO 4 ).

[0024] The positive electrode solvent is an NMP (N-methyl-2-pyrrolidone) solution, which is an example of an organic solvent. The positive electrode conductive material is, for example, carbon black such as acetylene black or ketjen black, carbon fiber such as carbon nanotube or carbon nanofiber, or graphite. The positive electrode binder is an example of a resin component contained in the positive electrode mixture paste. The positive electrode binder is, for example, polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), styrene butadiene rubber (SBR), or the like.

[0025] The positive electrode sheet 21 may have an insulating layer at the boundary between the positive electrode uncoated portion 22A and the positive electrode mixture layer 23. The insulating layer contains an inorganic component having insulating properties and a resin component that functions as a binder. The inorganic component is at least one selected from the group consisting of powdered boehmite, titania, and alumina. The resin component is at least one selected from the group consisting of PVDF, PVA, and acrylic.

[0026] [Negative electrode sheet 24] The negative electrode sheet 24 includes a negative electrode current collector 25 and a negative electrode composite layer 26. The negative electrode current collector 25 is a foil-like negative electrode base material formed in an elongated shape. The negative electrode composite layer 26 is provided on each of two opposing surfaces of the negative electrode current collector 25. The negative electrode current collector 25 includes a negative electrode-side uncoated portion 25A at one end in the width direction D2, which is located opposite the positive electrode-side uncoated portion 22A, where the negative electrode composite layer 26 is not formed and the negative electrode current collector 25 is exposed.

[0027] A metal foil made of copper or an alloy mainly composed of copper is used for the negative electrode current collector 25. The negative electrode current collector 25 functions as a current collector for the negative electrode. In the wound body state, the negative electrode uncoated portion 25A has opposing surfaces pressed against each other to form the negative electrode current collector 20B.

[0028] The negative electrode mixture layer 26 is a hardened body of the liquid negative electrode mixture paste. The negative electrode mixture paste includes a negative electrode active material, a lithium salt, a negative electrode solvent, a negative electrode thickener, and a negative electrode binder. The negative electrode mixture layer 26 is formed by drying the negative electrode mixture paste and evaporating the negative electrode solvent. Therefore, the negative electrode mixture layer 26 includes the negative electrode active material, the lithium salt, and further includes a negative electrode thickener and a negative electrode binder as additives. The negative electrode mixture layer 26 may further include an additive such as a conductive material.

[0029] The negative electrode active material is a material capable of absorbing and releasing lithium ions. Examples of the negative electrode active material include carbon materials such as graphite, non-graphitizable carbon, graphitizable carbon, and carbon nanotubes. The negative electrode solvent is, for example, water. The lithium salt is LiPF 6 , LiBF 4 , LiClO 4 , LiAsF 6 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiN(CF 3 SO 2 ) 2 , LiC(CF 3 SO 2 ) 3 One or more lithium compounds (lithium salts) selected from LiI, LiBOB (lithium bis(oxalato)borate), etc. can be used. In this embodiment, LiBOB is used as the lithium salt. As the negative electrode thickener, for example, CMC (carboxymethyl cellulose) can be used as a thickener containing a sodium salt. As the negative electrode binder, the same material as the positive electrode binder can be used. As the negative electrode binder, for example, SAR (styrene acrylic acid copolymer) can be used as a binder containing a sodium salt.

[0030] [Separator 27] The separator 27 prevents contact between the positive electrode sheet 21 and the negative electrode sheet 24, and retains a nonaqueous electrolyte between the positive electrode sheet 21 and the negative electrode sheet 24. When the electrode body 20 is immersed in the nonaqueous electrolyte, the nonaqueous electrolyte permeates from the ends of the separator 27 in the width direction D2 toward the center.

[0031] The separator 27 is a nonwoven fabric made of polypropylene, etc. As the separator 27, for example, a porous polymer membrane such as a porous polyethylene membrane, a porous polyolefin membrane, a porous polyvinyl chloride membrane, an ion-conductive polymer electrolyte membrane, etc. can be used.

[0032] [Nonaqueous electrolyte] The non-aqueous electrolyte is a composition in which a supporting salt is contained in a non-aqueous solvent. As the non-aqueous solvent, one or more materials selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, etc. can be used. In this embodiment, ethylene carbonate is used as the non-aqueous solvent. The supporting salt is LiPF 6 , LiBF 4 , LiClO 4 , LiAsF 6 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiN(CF 3 SO 2 ) 2 , LiC(CF 3 SO 2 ) 3 In this embodiment, one or more lithium compounds (lithium salts) selected from LiPF , LiI, etc. can be used as the supporting salt. 6 In this embodiment, the nonaqueous electrolyte does not contain LiBOB, which is a film-forming material containing a lithium salt.

[0033] [Manufacturing method] Next, a method for manufacturing the lithium ion secondary battery 10 will be described with reference to Fig. 3 to Fig. 6. The method for manufacturing the lithium ion secondary battery 10 includes a coating step and a liquid injection step.

[0034] [Coating process] In the coating step, the negative electrode composite paste is applied in two layers to the negative electrode current collector 25. Therefore, the coating step includes a first coating step and a second coating step. In the coating step, the coating is performed such that the amount of lithium salt contained in the negative electrode composite layer 26 is smaller on the surface side of the negative electrode composite layer 26 than on the current collector side closer to the negative electrode current collector 25.

[0035] As shown in FIG. 3, in the first coating step, the first negative electrode mixture layer 26A containing the lithium salt 32 is coated on the negative electrode current collector 25. The diameter of the lithium salt 32 is 0.414 times or less the diameter of the negative electrode active material 31. The diameters of the lithium salt 32 and the negative electrode active material 31 are average particle diameters. This condition is a condition for the lithium salt 32 to slip through the gaps of the negative electrode active material 31 and move after the nonaqueous electrolyte is injected. That is, if the particles of the lithium salt 32 are large, the contact points between the negative electrode active materials 31 are reduced, and the packing efficiency of the negative electrode active material 31 is reduced, thereby reducing the peel strength. In FIG. 3, the negative electrode active material 31 and the lithium salt 32 contained in the first negative electrode mixture layer 26A are illustrated in a simplified manner. The thickness of the first negative electrode mixture layer 26A is approximately the same as the sum of the diameters of the two negative electrode active materials 31.

[0036] As shown in FIG. 4, in the second coating step, the second negative electrode mixture layer 26B not including the lithium salt 32 is coated on the first negative electrode mixture layer 26A. That is, the second negative electrode mixture layer 26B has a smaller amount of lithium salt than the first negative electrode mixture layer 26A. The thickness of the second negative electrode mixture layer 26B is approximately twice the thickness of the negative electrode active material 31. The negative electrode mixture layer 26 is composed of the first negative electrode mixture layer 26A and the second negative electrode mixture layer 26B. The thickness of the negative electrode mixture layer 26 is approximately the same as the sum of the diameters of the four negative electrode active materials 31. Thus, the negative electrode sheet 24 is manufactured by coating the negative electrode current collector 25 with the negative electrode mixture layer 26.

[0037] [Liquid injection process] In the liquid injection step, a non-aqueous electrolyte solution that does not contain a film-forming material containing a lithium salt is injected into the battery case 11 that houses the positive electrode sheet 21 and the negative electrode sheet 24.

[0038] 4, in the liquid injection step, the nonaqueous electrolyte permeates from both ends of the negative electrode sheet 24 toward the center. At this time, if lithium salt 32 is present on the surface side of the negative electrode mixture layer 26, the lithium salt 32 moves from the ends to the center as the nonaqueous electrolyte permeates. However, in this embodiment, since the second negative electrode mixture layer 26B does not contain lithium salt 32, it is possible to prevent the lithium salt 32 from moving from the ends to the center together with the nonaqueous electrolyte.

[0039] As shown in Figures 5 and 6, when the nonaqueous electrolyte solution permeates from the surface of the negative electrode mixture layer 26 to the negative electrode current collector 25, the lithium salt 32 present in the first negative electrode mixture layer 26A also migrates to the surface side of the negative electrode mixture layer 26, and the lithium salt 32 spreads throughout the entire negative electrode mixture layer 26.

[0040] In this way, the migration of lithium salt 32 from the ends to the center is suppressed during injection of the nonaqueous electrolyte, and the lithium salt 32 is allowed to spread throughout the entire negative electrode mixture layer 26 after injection, allowing a coating derived from lithium salt 32 to be uniformly formed on the surface of the negative electrode mixture layer 26.

[0041] [effect] Next, the effects of this embodiment will be described. (1) The negative electrode mixture layer 26 is coated so that the amount of lithium salt 32 contained in the negative electrode mixture layer 26 is smaller on the surface side than on the collector side closer to the negative electrode current collector 25. Therefore, when a non-aqueous electrolyte containing lithium salt 32 and not containing a coating material is poured into the battery case 11, the lithium salt 32 on the surface side of the negative electrode mixture layer 26 can be prevented from migrating from the end portion to the center of the negative electrode sheet 24 by the non-aqueous electrolyte. The lithium salt 32 migrates from the negative electrode mixture layer 26 on the collector side closer to the negative electrode current collector 25 to the surface side, improving the uniformity of the coating derived from the lithium salt 32 of the negative electrode sheet 24. Therefore, the peel strength of the negative electrode mixture layer 26 can be prevented from decreasing.

[0042] (2) No lithium salt is contained on the current collector side of negative electrode mixture layer 26 close to negative electrode current collector 25. For this reason, unevenness in the film caused by lithium salt 32 formed on the surface of negative electrode mixture layer 26 can be suppressed.

[0043] (3) The method includes a first coating step of coating a first negative electrode mixture layer 26A onto a negative electrode current collector 25, and a second coating step of coating a second negative electrode mixture layer 26B, which has a smaller amount of lithium salt 32 than the first negative electrode mixture layer 26A, onto the first negative electrode mixture layer 26A. Therefore, the amount of lithium salt 32 contained in the negative electrode mixture layer 26 can be easily changed for each coating step.

[0044] (4) No lithium salt is contained in second negative electrode mixture layer 26B forming the surface of negative electrode mixture layer 26. For this reason, unevenness in the film resulting from lithium salt 32 formed on the surface of negative electrode mixture layer 26 can be suppressed.

[0045] (5) The diameter of the lithium salt 32 is 0.414 or less times the diameter of the negative electrode active material 31. Therefore, a decrease in the peel strength of the film originating from the lithium salt 32 can be suppressed.

[0046] [Other embodiments] The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other to the extent that no technical contradiction occurs.

[0047] In the above embodiment, the diameter of the lithium salt 32 is set to 0.414 or less times the diameter of the negative electrode active material 31. However, the diameter of the lithium salt 32 may be set to more than 0.414 times the diameter of the negative electrode active material 31 as long as a decrease in the peel strength of the negative electrode mixture layer 26 can be suppressed.

[0048] In the above embodiment, the second negative electrode mixture layer 26B does not contain the lithium salt 32. However, the second negative electrode mixture layer 26B may contain a smaller amount of lithium salt 32 than the first negative electrode mixture layer 26A.

[0049] In the above embodiment, the negative electrode mixture layer 26 is a two-layer coating consisting of the first negative electrode mixture layer 26A and the second negative electrode mixture layer 26B. However, the negative electrode mixture layer 26 may be formed by coating three or more layers as long as the amount of lithium salt 32 is less on the surface side of the negative electrode mixture layer 26 than on the collector side closer to the negative electrode current collector 25. For example, as shown in FIG. 7, the first negative electrode mixture layer 26A may be coated on the negative electrode current collector 25, the second negative electrode mixture layer 26B may be coated on the first negative electrode mixture layer 26A, and the third negative electrode mixture layer 26C may be coated on the second negative electrode mixture layer 26B. In this case, the second negative electrode mixture layer 26B has a smaller amount of lithium salt 32 than the first negative electrode mixture layer 26A, and the third negative electrode mixture layer 26C has a smaller amount of lithium salt 32 than the second negative electrode mixture layer 26B. Note that the first negative electrode mixture layer 26A may contain the lithium salt 32, and the second negative electrode mixture layer 26B and the third negative electrode mixture layer 26C may not contain the lithium salt 32. The first negative electrode mixture layer 26A, the second negative electrode mixture layer 26B, and the third negative electrode mixture layer 26C each have a thickness equivalent to approximately one particle of the negative electrode active material 31.

[0050] In the above embodiment, the thickness of each of the first negative electrode mixture layer 26A and the second negative electrode mixture layer 26B is set to be substantially equal to the sum of the diameters of two negative electrode active material particles 31. However, the thickness of each of the first negative electrode mixture layer 26A and the second negative electrode mixture layer 26B may be set to be substantially equal to the sum of the diameter of one negative electrode active material particle 31, as shown in FIG. 7. The thickness of the negative electrode mixture layer 26 may be set independently of the diameter of the negative electrode active material particle 31.

[0051] In the above embodiment, LiBOB is added as the lithium salt to the negative electrode mixture layer 26. However, the lithium salt is not limited to LiBOB. In the above embodiment, the electrode body 20 is a wound body obtained by winding a laminate in which the positive electrode sheet 21 and the negative electrode sheet 24 are laminated with the separator 27 interposed therebetween. However, the electrode body may be a laminate in which a plurality of positive electrode sheets 21 and a plurality of negative electrode sheets 24 are alternately stacked with the separator 27 interposed therebetween.

[0052] The lithium ion secondary battery 10 may be mounted on an automatic transport vehicle, a special vehicle for loading and unloading, an electric vehicle, a hybrid vehicle, a computer, or other electronic device, or may be part of other systems. For example, it may be mounted on a moving object such as a ship or an aircraft, or may be a power supply system that supplies power from a power plant via a substation to a building or home in which a secondary battery is installed.

[0053] [Example] Next, examples and comparative examples of the lithium ion secondary battery 10 will be described with reference to Fig. 8. Note that these examples and comparative examples are not intended to limit the scope of non-aqueous secondary batteries.

[0054] 8, lithium ion secondary batteries 10 were prepared in examples and comparative examples in which the combination of the addition position of lithium salt 32 added to negative electrode mixture layer 26 and the diameter ratio of lithium salt 32 added to negative electrode mixture layer 26 to negative electrode active material 31 was changed. Then, for each example and comparative example, the uniformity of the coating derived from the lithium salt and the peel strength of negative electrode mixture layer 26 were evaluated using Comparative Example 1 as a reference.

[0055] [Comparative Example 1] The lithium salt 32 added to the negative electrode mixture layer 26 was added to the upper layer, i.e., the lithium salt 32 was added only to the second negative electrode mixture layer 26B, and the diameter ratio of the lithium salt 32 added to the negative electrode mixture layer 26 to the negative electrode active material 31 was set to 0.4.

[0056] [Comparative Example 2] The lithium salt 32 added to the negative electrode mixture layer 26 was added to the lower layer, i.e., the lithium salt 32 was added only to the first negative electrode mixture layer 26A, and the diameter ratio of the lithium salt 32 added to the negative electrode mixture layer 26 to the negative electrode active material 31 was set to 0.75.

[0057] [Example 1] The lithium salt 32 added to the negative electrode mixture layer 26 was added to the lower layer, i.e., the lithium salt 32 was added only to the first negative electrode mixture layer 26A, and the diameter ratio of the lithium salt 32 added to the negative electrode mixture layer 26 to the negative electrode active material 31 was set to 0.4.

[0058] [Example 2] The lithium salt 32 added to the negative electrode mixture layer 26 was added to the lower layer, i.e., the lithium salt 32 was added only to the first negative electrode mixture layer 26A, and the diameter ratio of the lithium salt 32 added to the negative electrode mixture layer 26 to the negative electrode active material 31 was set to 0.25.

[0059] [evaluation] For each of the above examples and comparative examples, the uniformity of the coating derived from lithium salt 32 and the peel strength of negative electrode mixture layer 26 were evaluated. The uniformity of the coating derived from lithium salt 32 is a value obtained by dividing the amount of the coating derived from lithium salt 32 near the end of negative electrode sheet 24 by the overall average amount of the coating derived from lithium salt 32 on negative electrode sheet 24.

[0060] In Comparative Example 2 and Examples 1 and 2, in which the lithium salt 32 is added to the negative electrode mixture layer 26 at the lower layer, the uniformity of the coating derived from the lithium salt 32 is higher than that of Comparative Example 1, and the peel strength of the negative electrode mixture layer 26 is lower than that of Comparative Example 1.

[0061] In Comparative Example 2, in which the diameter ratio of the lithium salt 32 added to the negative electrode mixture layer 26 to the negative electrode active material 31 is greater than 0.414 times, the uniformity of the coating derived from the lithium salt 32 is higher than that of Comparative Example 1, while the peel strength of the negative electrode mixture layer 26 is significantly lower than that of Comparative Example 1. In Examples 1 and 2, in which the diameter ratio of the lithium salt 32 added to the negative electrode mixture layer 26 to the negative electrode active material 31 is 0.414 times or less, the uniformity of the coating derived from the lithium salt 32 is higher than that of Comparative Example 1, and it is possible to suppress a significant decrease in the peel strength of the negative electrode mixture layer 26 from that of Comparative Example 1. Therefore, it is desirable that the addition position of the lithium salt 32 added to the negative electrode mixture layer 26 is the lower layer, and the diameter ratio of the lithium salt 32 added to the negative electrode mixture layer 26 to the negative electrode active material 31 is 0.414 times or less. In Examples 1 and 2, excellent results were obtained. [Explanation of symbols]

[0062] 10...Lithium-ion secondary battery 11…Battery case 12…Lid body 13A…Positive external terminal 13B…Negative external terminal 14A…Positive electrode side current collecting member 14B: Negative electrode side current collecting member 20...Electrode body 20A…Positive electrode current collector 20B: Negative electrode current collector 21...Positive electrode sheet 22...Positive electrode current collector 22A: Positive electrode uncoated area 23...Positive electrode mixture layer 24...Negative electrode sheet 25...Negative electrode current collector 25A…Negative electrode uncoated area 26…Negative electrode composite material layer 26A…First negative electrode composite layer 26B...Second negative electrode composite layer 26C...Third negative electrode composite layer 27…Separator 31...Negative electrode active material 32...Lithium salt

Claims

1. A method for manufacturing a non-aqueous secondary battery having a positive electrode sheet, a negative electrode sheet, and a non-aqueous electrolyte solution, comprising the steps of: a coating step of coating a negative electrode mixture layer containing a negative electrode active material and a lithium salt onto a negative electrode substrate to produce the negative electrode sheet; a liquid injection step of injecting the nonaqueous electrolyte solution not containing the coating material containing a lithium salt into a battery case containing the positive electrode sheet and the negative electrode sheet, In the coating step, the negative electrode mixture layer is coated so that the amount of the lithium salt contained therein is smaller on the surface side of the negative electrode mixture layer than on the substrate side closer to the negative electrode substrate. A method for manufacturing a non-aqueous secondary battery.

2. The surface side of the negative electrode mixture layer does not contain the lithium salt. The method for producing the nonaqueous secondary battery according to claim 1 .

3. The coating step includes a first coating step of coating a first negative electrode mixture layer containing the lithium salt onto the negative electrode base material; and a second coating step of coating the first negative electrode mixture layer with a second negative electrode mixture layer having a smaller amount of the lithium salt than the first negative electrode mixture layer. The method for producing the nonaqueous secondary battery according to claim 1 .

4. The second negative electrode mixture layer forms a surface of the negative electrode mixture layer and does not contain the lithium salt. The method for producing the nonaqueous secondary battery according to claim 3 .

5. The diameter of the lithium salt is 0.414 times or less than the diameter of the negative electrode active material. The method for producing the nonaqueous secondary battery according to any one of claims 1 to 4.

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